Non-duplexer architectures for telecommunications system

ABSTRACT

A telecommunications system can include analog-to-digital converters in an uplink communication path or a downlink communication path. The analog-to-digital converters can have a high dynamic range and bandwidth to obviate a need for down-conversion of signals using an analog mixer. The uplink communication path and the downlink communication path can be coupled to an antenna using a non-duplexer coupling device. Uplink signals traversing the uplink communication path can be isolated from downlink signals independent of using a duplexer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/579,181 titled “NON-DUPLEXER ARCHITECTURES FORTELECOMMUNICATIONS SYSTEM” and filed on Dec. 1, 2017, which is a 371National Stage Application of PCT Application No. PCT/IB2015/057404,filed on Sep. 25, 2015 and titled “NON-DUPLEXER ARCHITECTURES FORTELECOMMUNICATIONS SYSTEM”, which claims priority to U.S. ProvisionalApplication Ser. No. 62/155,585, filed May 1, 2015 and titled“Distributed Antenna System with Non-Duplexer Isolator Subsystem,” thecontents of each of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates generally to telecommunications and moreparticularly (although not necessarily exclusively) to isolating anuplink communication path from a downlink communication path in adistributed antenna system without the use of a duplexer.

BACKGROUND

A telecommunications system can include a distributed antenna system(“DAS”) or a repeater that can be used to extend the coverage of acellular communication system. For example, a DAS can extend coverage toareas of traditionally low signal coverage within buildings, tunnels, orin areas obstructed by terrain features. A DAS can include one or moremaster units in communication with carrier systems, such as basetransceiver stations of cellular service providers. The DAS can alsoinclude remote units physically separated from the master unit, but incommunication with the master unit via a serial link that may be copper,optical, or other suitable communication medium.

The remote units can wirelessly communicate with user devices positionedin a coverage area. For example, the remote units can be positioned in abuilding, tunnel, or other structure that prevents or limitscommunications directly with the carriers. Remote units amplify downlinksignals received from the base station via a master unit and radiate thedownlink signal using an antenna. An antenna unit recovers uplinksignals from mobile user equipment and provides the uplink signals tothe master unit. The uplink signals can be summed together and providedback to the base station.

A remote unit can include at least one duplexer. The duplexer canisolate a transmitter output from a receiver input by allowingfrequencies within the downlink band to be provided from the transmitteroutput to the antenna and allowing frequencies within the uplink band tobe provided from the antenna output to the receiver. But, duplexers canprovide little or no flexibility to respond to changes in frequency bandallocation.

SUMMARY

According to one aspect of the present disclosure, a telecommunicationssystem can include an uplink communication path and a downlinkcommunication path coupled to an antenna. Analog-to-digital converterscan be positioned in the uplink communication path and the downlinkcommunication path. The analog-to-digital converters can have a dynamicrange and bandwidth for sampling a signal prior to down-converting thesignal. The telecommunication system can isolate uplink signalstraversing the uplink communication path from downlink signalstraversing the downlink communication path without using a duplexer.

According to another aspect of the present disclosure, atelecommunications system can include a master unit and a remote unit.The master unit can include an analog-to-digital converter having adynamic range and bandwidth for sampling downlink signals prior todown-converting the downlink signals. The remote unit can include anuplink communication path and a downlink communication path coupled toan antenna. The remote unit can isolate uplink signals traversing theuplink communication path from the downlink signals traversing thedownlink communication path without using a duplexer.

According to another aspect of the present disclosure, a method caninclude coupling an antenna to an uplink communication path and adownlink communication path using a power combiner. The method may alsoinclude converting downlink signals traversing the downlinkcommunication path from analog signals to digital signals using ananalog-to-digital converter. The analog-to-digital converter may have adynamic range and bandwidth for sampling the analog signals prior todown-converting, using an analog mixer, the analog signals. The methodcan also include isolating uplink signals traversing the uplinkcommunication path from the downlink signals without using a duplexer.

These illustrative aspects and features are mentioned not to limit ordefine the invention, but to provide examples to aid understanding ofthe inventive concepts disclosed in this application. Other aspects,advantages, and features of the present invention will become apparentafter review of the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of an environment for atelecommunications system for isolating uplink signals from downlinksignals without using a duplexer according to one aspect.

FIG. 2 is a block diagram of a system for isolating uplink signals fromdownlink signals without using a duplexer that can be disposed in thetelecommunications system of FIG. 1 according to one aspect.

FIG. 3 is a schematic view of a system that includes a power combinerfor coupling an antenna to a downlink communication path and an uplinkcommunication path according to one aspect.

FIG. 4 is a schematic view of a system including a configurable analogfilter for active analog mitigation according to one aspect.

FIG. 5 is a schematic view of a system including a configurable digitalfilter for active digital mitigation according to one aspect.

FIG. 6 is a schematic view of a system including a configurable digitalfilter and additional active mitigation circuitry according to oneaspect.

FIG. 7 is a schematic view of a system including two configurabledigital filters for active digital mitigation according to one aspect.

FIG. 8 is a schematic view of a system including three configurabledigital filters for active digital mitigation according to one aspect.

DETAILED DESCRIPTION

Certain aspects and features are directed to a telecommunications systemfor isolating uplink signals traversing an uplink communication path inthe system from downlink signals using high dynamic rangeanalog-to-digital converters in an active mitigation subsystem,obviating the need for a duplexer in the DAS. The analog-to-digitalconverters can have a very high dynamic range and bandwidth to allow forconverting analog signals to digital signals without priordown-conversion of the analog signals. The use of theseanalog-to-digital converters in the telecommunications system can reduceor eliminate the need for the down-conversion of signals using an analogmixer. Down-conversion using an analog mixer can often be a major sourceof spurious responses necessitating strict isolation requirements insome DAS architectures. Reducing or eliminating some of the strictrequirements for isolation of the uplink signals from the downlinksignals can allow for a coupling device having little inherent isolationproperties (e.g., a power combiner) to be used for coupling the uplinkcommunication path to a downlink communication path. The uplinkcommunication path and the downlink communication path may be coupled toan antenna.

FIG. 1 schematically depicts a DAS 100 that can include a system forisolating uplink signals from downlink signals without using a duplexeraccording to an aspect of the present disclosure. The DAS 100 can becommunicatively coupled to at least one base station 102 via a wired orwireless communication medium. The DAS 100 can be positioned in an areasuch as a building environment to extend wireless communicationcoverage. The DAS 100 can include one or more remote units 104 that aredistributed in the environment to provide coverage within a service areaof the DAS 100. The remote units 104 can service a number of differentuser devices 106, such as cellular phones, operating in the environmentof the DAS 100. Each remote unit 104 can include at least one antenna108. Antenna 108 may be a common antenna or can include one or moreantenna elements.

Remote units 104 can be communicatively coupled to one or more masterunits 110 via any communication medium capable of carrying signalsbetween the master unit 110 and remote unit 104. Examples of suitablecommunication mediums include copper, optical, and microwave link.Master units 110 can process the signals from remote units 104 tointerface appropriately with the base station 102. A system controller112 can control the operation of each of the master units 110 forprocessing the signals 114 associated with the remote units 104. Thesignals 114 of the remote units 104 can be the uplink and downlinksignals of the DAS 100 for communicating with user devices 106.

Although DAS 100 is depicted as including two master units 110 and fourremote units 104, any number (including one) of each of master units 110and remote units 104 can be used. Furthermore, a DAS 100, according tosome aspects, can be implemented without system controller 112. Thepresent disclosure can be included in one or more of the remote units

FIG. 2 depicts a telecommunications system in DAS 100 including anactive mitigation subsystem 200, a downlink communication path 202, andan uplink communication path 204. Circuitry included in the activemitigation subsystem 200 can be included in the downlink communicationpath 202 and the uplink communication path 204 and can isolate signalstraversing the uplink communication path 204 from signals or othersignal components of the downlink communication path 202. Downlinkcommunication path 202 and uplink communication path 204 can becommunicatively coupled to antenna 108. In some aspects, downlinkcommunication path 202 and uplink communication path 204 can be directlycoupled to antenna 108 by a device having little inherent isolation(e.g., a power combiner). Antenna 108 can include one antenna that canboth transmit and receive RF signals.

In some aspects, active mitigation subsystem 200 can be disposed in aremote unit 104. In other aspects, active mitigation subsystem 200 canbe disposed in a master unit 110. The active mitigation subsystem 200can alternatively be disposed throughout various components of the DAS100 (e.g., partially within a master unit 110 and partially within aremote unit 104).

The circuitry included in the active mitigation subsystem 200 accordingto various aspects can incorporate components that prevent the formationof a feedback loop. These components can attenuate the gain of bothuplink and downlink signal to prevent system instability in DAS 100.

FIG. 3 schematically depicts circuitry for an active mitigationsubsystem 200 with the downlink communication path 202 and uplinkcommunication path 204 coupled to antenna 108 by a power combiner 300.Antenna 108 can radiate downlink signals traversing downlinkcommunication path 202 to user devices 106. Antenna 108 can also recoveruplink signals from user devices 106 and can provide the uplink signalsto the uplink communication path 204. Signals traversing uplinkcommunication path 204 can be provided to base station 102.

The active mitigation subsystem 200 can include anti-aliasing filter302, analog-to-digital converter 304, digital IF filter 306,digital-to-analog converter 308, analog filter 310, mixer 312, localoscillator 314, power amplifier 316, and electronically tuned filter 318in the downlink communication path 202. Anti-aliasing filter 302 canreduce aliasing from converting the downlink signal from analog todigital. For example, anti-aliasing filter 302 can restrict signalbandwidths to one Nyquist zone, rejecting frequencies occupyingbandwidths greater than one-half the sampling frequency ofanalog-to-digital converter 304. Anti-aliasing filter 302 can alsoreject signal components in one or more adjacent Nyquist zones. In someaspects, anti-aliasing filter 302 can include a surface acoustic wave(“SAW”) filter. Analog-to-digital converter 304 can convert the analogdownlink signal to a digital downlink signal, such as for transmissionvia a serial link between a master unit, which includes theanalog-to-digital converter 304, and a remote unit. In some aspects,analog-to-digital converter 304 can be a very high dynamic rangeanalog-to-digital converter. Analog-to-digital converter 304 can includea sample rate and input bandwidth sufficient to directly sample incomingRF signals from base station 102. For example, an analog-to-digitalconverter with an input bandwidth greater than 1 GHz and sample rategreater than 2 GHz would be sufficient to directly sample allfrequencies up to 1 GHz. Use of a very high dynamic rangeanalog-to-digital converter bypasses the need for down-conversion of adownlink signal in downlink communication path 202 prior toanalog-to-digital converter 304 converting the downlink signal to adigital downlink signal.

Digital IF filter 306 can receive the digital downlink signal and reducethe bandwidth of the downlink digital signal. Digital-to-analogconverter 308 can convert the downlink signal to an analog signal.Analog filter 310 can receive the analog downlink signal and remove anyaliases resulting from converting the digital signals to analog. Mixer312 and local oscillator 314 can up-convert the downlink signal to theappropriate RF frequency. Power amplifier 316 can amplify the downlinksignal to the output power for transmission.

Prior to antenna 108 broadcasting the downlink signal, electronicallytuned filter 318 can attenuate any undesirable signals generated in thetransmitter. Attenuation of undesirable signals can preventdesensitization of a receiver from transmitted noise falling in thereceive frequency band of antenna 108. Attenuation of undesirablesignals can also prevent spurious signals generated in a transmitter atreceive frequency bands from entering the receiver. Undesirable signalcomponents can be generated by components of downlink communication path202 while processing the downlink signal, or otherwise. Undesirablesignal components can include signals, other than the desired downlinksignal, transmitted by transmit antenna 108 at a frequency within thereceive frequency band of antenna 108. Undesirable signal components canalso include harmonics of the transmit RF frequency of downlink signals.Undesirable signal components can also include signals generated bymixer 312 and local oscillator 314 during up-conversion to RF. Forexample, during up-conversion, mixer 312 can process the IF downlinksignal and a signal received from local oscillator 314. The outputsignal of mixer 312 can include two signals. One signal may be the RFdownlink signal at a frequency equal to the sum of the frequencies ofthe IF downlink signal and the signal received from local oscillator314. The other signal can be an image signal at a frequency equal to thedifference of the frequencies of the IF downlink signal and the signalreceived from local oscillator 314. The image signal, as well as anyharmonics of the output signals of mixer 312, may be undesirable signalcomponents.

In some aspects, some components positioned in the downlinkcommunication path 202 can be disposed in master unit and othercomponents can be disposed within a remote unit. The components disposedin a master unit can include anti-aliasing filter 302 andanalog-to-digital converter 304. The components disposed within a remoteunit can include digital IF filter 306, digital-to-analog converter 308,analog filter 310, mixer 312, local oscillator 314, power amplifier 316,and electronically tuned filter 318. In these aspects, the output ofanalog-to-digital converter 304 is coupled to the input of digital IFfilter 306 via a serial communications link. In other aspects, allcomponents of downlink communication path 202 can be disposed in amaster unit or in a remote unit. Although FIG. 3 depicts the downlinkcommunication path 202 receiving signals directly from the base station102, a downlink communication path 202 can receive signals from a basestation 102 via one or more intermediate components or devices. Forexample, the downlink communication path 202 can receive signals from abase station 102 via a master unit when all of the components of adownlink communication path 202 are disposed in a remote unit.

The active mitigation subsystem 200 can include anti-aliasing filter320, analog-to-digital converter 322, digital IF filter 324,digital-to-analog converter 326, analog filter 328, local oscillator332, mixer 330, power amplifier 334, and uplink gain adjust device 336in the uplink communication path 204. Antenna 108 can recover uplinksignals from a mobile user device 106 and provide uplink signals toanti-aliasing filter 320. Anti-aliasing filter 320 can reject signalcomponents of bandwidths greater than one-half the sampling frequency ofanalog-to-digital converter 322, as well as frequencies within one ormore adjacent Nyquist zones, to reduce aliasing from converting theuplink signal from analog to digital. In some aspects, anti-aliasingfilter 320 can be a surface acoustic wave (“SAW”) filter.Analog-to-digital converter 322 can convert the analog uplink signal toa digital uplink signal that can be transmitted over a serial link froma remote unit to a master unit. In some aspects, analog-to-digitalconverter 322 can be a very high dynamic range analog-to-digitalconverter. Analog-to-digital converter 322, similar to analog-to-digitalconverter 304, can include sample rates and input bandwidths sufficientto directly sample incoming RF signals received by antenna 108. Use of avery high dynamic range analog-to-digital converter bypasses the needfor down-conversion of an uplink signal in uplink communication path 204prior to analog-to-digital converter 322 converting the downlink signalto a digital downlink signal.

Digital IF filter 324 can further limit the bandwidth of the uplinksignal. Digital-to-analog converter 326 can convert the uplink digitalsignal to an analog signal. Analog filter 328 can filter the signal toprevent aliasing that can result from converting the digital signals toanalog. Local oscillator 332 and mixer 330 can up-convert the uplinksignal to RF for transmission to the base station 102. Power amplifier334 can amplify the uplink signal prior to transmission to base station102. Uplink gain adjust device 336 can compensate for transmitter noiseon the uplink signal. For example, uplink gain adjust device 336 canincrease the uplink signal gain to ensure that the signal-to-noise ratioof the uplink signal does not decrease below an acceptable threshold.The uplink signal from gain adjust device 336 can be provided to thebase station 102.

In some aspects, some components positioned in the uplink communicationpath 204 are disposed in a master unit and other components of uplinkcommunication path 204 are disposed in a remote unit. The componentsdisposed in a remote unit can include anti-aliasing filter 320 andanalog-to-digital converter 322. The components disposed in a masterunit can include digital IF filter 324, digital-to-analog converter 326,analog filter 328, mixer 330, local oscillator 332, power amplifier 334,and uplink gain adjust device 336. Analog-to-digital converter 322 canbe serially coupled to digital IF filter 324. Although FIG. 3 depictsthe uplink communication path 204 providing signals directly to the basestation 102, an uplink communication path 204 can provide signals to abase station 102 via one or more intermediate components or devices. Forexample, the uplink communication path 204 can provide signals to a basestation 102 via a master unit when all components of an uplinkcommunication path 204 are disposed in a remote unit. In some aspects,the uplink communication path 204 can include a digital summer in amaster unit. The digital summer can be communicatively coupled to theoutput of digital IF filter 324. The digital summer can sum uplinksignals from various remote units before providing the uplink signals tothe base station 102.

The use of very high dynamic analog-to-digital converters (e.g.,analog-to-digital converters 304, 322) in the active mitigationsubsystem 200 can allow for power combiner 300 or any other couplingdevice having little inherent isolation to directly couple downlinkcommunication path 202 and uplink communication path 204 to antenna 108.The spurious responses due to down-conversion are no longer present asthe analog-to-digital converters can obviate the need fordown-conversion of the signals. This prevents a number of issuesnormally addressed by duplexers or other coupling devices having higherisolation properties. For example, obviating a need for down-conversioncan: prevent damage of receiver input stages, prevent signals generatedin a transmitter that can fall at other frequencies at which a receiverwould be susceptible if a receive down-converter were present (e.g.,images, mixed spurious products, etc.) from interfering with the desiredsignal, prevent the creation of spurious receiver responses from strongtransmit signals which may enter the receiver, which would otherwise becreated if a receive down-converter were present (e.g., due tointermodulation), and prevent clipping of the analog-to-digitalconverter in the uplink communication path in the case where thetransmitter and receiver use overlapping frequency bands (e.g., a timedivision duplex).

FIG. 4 schematically depicts active analog mitigation circuitry of theactive mitigation subsystem 200 positioned in uplink communication path204. The uplink communication path 204 can include active analogmitigation circuitry including a configurable analog filter 400 in areference path 402 and an analog summer 404 that receives a downlinkmitigation signal from the configurable analog filter 400. Referencepath 402 can include a path from a coupled point at the output of poweramplifier 316 to an input of the analog summer 404. A downlink referencesignal from the output of power amplifier 316 can traverse referencepath 402.

Configurable analog filter 400 can be positioned in the reference path402 and communicatively coupled to power amplifier 316 to receive thedownlink reference signal. Configurable analog filter 400 can generate adownlink mitigation signal from the downlink reference signal byadjusting the gain and shifting the phase of the downlink referencesignal. The downlink mitigation signal can be equal in amplitude to, and180 degrees out of phase with, undesirable signal components generatedin downlink communication path 202 and recovered by antenna 108.

Analog summer 404 can be positioned in the uplink communication path204. The output of configurable analog filter 400 can be communicativelycoupled to one of the inputs of analog summer 404. Another input ofanalog summer 404 can be communicatively coupled to antenna 108. Analogsummer 404 can receive the downlink mitigation signal from theconfigurable analog filter 400 and sum the downlink mitigation signalwith the uplink signal to mitigate any undesirable signal componentspresent in the uplink signal. Mitigating undesirable signal componentscan include, for example, cancelling the undesirable downlink signalcomponents present in the uplink signal. Analog summer 404 can providethe uplink signal to anti-aliasing filter 320. The uplink signal cantraverse the remainder of uplink communication path 204 as depicted inFIG. 3.

The frequency response of configurable analog filter 400 can be set atset-up of the DAS 100 using a test signal. For example, the test signalcan be transmitted by antenna 108 and any signal detected on uplinkcommunication path 204 can be identified as the undesirable signalcomponent generated by the transmission of the test downlink signal. Thefrequency response of configurable analog filter 400 can then beadjusted via electronic or manual processes to generate a downlinkmitigation signal equal in amplitude to and 180 degrees out of phasewith the undesirable signal component. In some aspects, configurableanalog filter 400 can include an analog vector modulator capable ofadjusting the phase and gain of the downlink mitigation signal.

In some aspects, configurable analog filter 400 can include an adaptivefilter. The adaptive filter can be dynamically optimized by amicroprocessor utilizing an iterative adaptation algorithm. The inputsto the iterative adaptation algorithm can be a downlink reference signal(e.g. the output signal from power amplifier 316) and an error signal(e.g. the output signal from analog summer 404). The microprocessor canapply the iterative adaptation algorithm to optimize the frequencyresponse of configurable analog filter 400. Configurable analog filter400, applying an optimized frequency response, can generate a downlinkmitigation signal correlated with the undesirable signal component fromdownlink communication path 202. In some aspects, the iterativeadaptation algorithm can be a least mean square algorithm.

FIG. 5 depicts active digital mitigation circuitry that can be includedin the active mitigation subsystem 200. The circuitry is positioned inthe downlink communication path 202, the uplink communication path 204,and a reference path 500. The active digital mitigation circuitry caninclude a digital summer 502 that receives a downlink mitigation signalfrom a configurable digital filter 504 in reference path 500.

FIG. 5 schematically depicts the components that can be included inuplink communication path 204 and the corresponding components that canbe included in reference path 500 in addition to configurable digitalfilter 504. Reference path 500 can include an analog IF filter 506 andan analog-to-digital converter 508. A downlink signal can traverse thedownlink communication path 202 as depicted in FIG. 4. The referencepath 500 can be a path from the output of power amplifier 316 to one ofthe inputs of digital summer 502. Power amplifier 316 can provide adownlink reference signal to configurable digital filter 504 viareference path 500. Analog IF filter 506 and analog-to-digital converter508 can process the downlink reference signal in the same manner astheir corresponding components along a parallel section of uplinkcommunication path 204 that process the uplink signal. In some aspects,analog-to-digital converter 508 can be a very high dynamic rangeanalog-to-digital converter. Analog-to-digital converter 508, similar toanalog-to-digital converters 322, can include sample rates and inputbandwidths sufficient to directly sample incoming RF reference downlinksignals received from the output of power amplifier 316. Use of a veryhigh dynamic range analog-to-digital converter bypasses the need fordown-conversion of a reference downlink signal in reference path 500prior to analog-to-digital converter 508 converting the referencedownlink signal to a digital reference downlink signal.

Configurable digital filter 504 can be positioned in the reference path500. Configurable digital filter 504 can receive a downlink referencesignal from analog-to-digital converter 508 and generate a downlinkmitigation signal. To generate the downlink mitigation signal,configurable digital filter 504 can adjust the gain and phase of thedownlink reference signal. The downlink mitigation signal can be equalin amplitude to and phase shifted 180 degrees from any undesirablesignal component generated on downlink communication path 202 andrecovered by antenna 108.

Digital summer 502 can be positioned in the uplink communication path204. The output of configurable digital filter 504 can becommunicatively coupled to one of the inputs of digital summer 502.Another input of digital summer 502 can be communicatively coupled tothe output of analog-to-digital converter 322. Digital summer 502 canreceive a downlink mitigation signal from configurable digital filter504 and a digital uplink signal from analog-to-digital converter 322.Digital summer 502 can sum the downlink mitigation signal with theuplink signal to mitigate any undesirable signal components present inthe uplink signal. In some aspects, digital summer 502 can provide theuplink signal to digital-to-analog converter 326. The uplink signal cantraverse the remainder of uplink communication path 204 as described inFIG. 3.

In some aspects, the active mitigation subsystem 200 can include one ormore devices for optimizing the frequency response of a configurabledigital filter, as depicted in FIGS. 6-8. Optimizing the frequencyresponse can allow the configurable digital filter to dynamicallygenerate an accurate downlink mitigation signal corresponding to anundesirable signal component. FIG. 6 shows downlink communication path202, uplink communication path 204, reference path 600, and antenna 108.Downlink communication path 202 can include digital-to-analog converter602, analog filter 604, mixer 606, local oscillator 608, and poweramplifier 610. Digital-to-analog converter 602 can convert digitaldownlink signals to analog signals. In some aspects, the digitaldownlink signals can be received from an analog-to-digital converter anddigital IF filter (e.g., analog-to-digital converter 304 and digital IFfilter shown in FIG. 3). Analog filter 604 can remove any aliasesresulting from converting the digital downlink signals to analogsignals. Mixer 606 and local oscillator 608 can up-convert downlinksignals to RF. Power amplifier 610 can amplify the downlink signal tothe output power for transmission.

Uplink communication path 204 can include anti-aliasing filter 612,analog-to-digital converter 614, and digital summer 616. Anti-aliasingfilter 612 can reject signal components at bandwidths greater thanone-half the sampling frequency of analog-to-digital converter 614, aswell as frequencies within one or more adjacent Nyquist zones, to reducealiasing from converting the uplink signal from analog to digital.Analog-to-digital converter 614 can convert the analog uplink signal toa digital uplink signal. In some aspects, analog-to-digital converter614 can be a very high dynamic range analog-to-digital converter.Analog-to-digital converter 614 can include sample rates and inputbandwidths sufficient to directly sample incoming RF uplink signalsreceived from antenna 108. Use of a very high dynamic rangeanalog-to-digital converter bypasses the need for down-conversion of anuplink signal in uplink communication path 204 prior toanalog-to-digital converter 614 converting the uplink signal to adigital uplink signal.

Digital summer 616 can sum the downlink mitigation signal fromconfigurable digital filter 618 with the uplink signal fromanalog-to-digital converter 614. Reference path 600 can includeattenuator 620, anti-aliasing filter 622, analog-to-digital converter624, and configurable digital filter 618. As depicted in FIG. 6, adownlink reference signal traversing reference path 600 can be used togenerate the downlink mitigation signal. Attenuator 620 can attenuatethe downlink reference signal such that the downlink reference signalpower at the input to anti-aliasing filter 622 is equal to the power ofany undesirable signals recovered by antenna 108 at the input toanti-aliasing filter 612. Equalizing the power of the downlink referencesignal and the undesirable signals recovered by antenna 108 can ensurethat the mitigation signal generated by configurable digital filter 618can mitigate non-linear distortion signals on uplink communication path204.

Attenuator 620 can attenuate the power of the downlink reference signalsuch that the ratio between the undesirable signal power and thenon-linear distortion signal power on uplink communication path 204 isequal to the ratio between the downlink reference signal power and thenon-linear distortion signal power on reference path 600. When theseratios are equal, the mitigation signal generated from the referencesignal can mitigate both the undesirable signals and the non-lineardistortion signal components on uplink communication path 204. Theattenuation provided by attenuator 620 can be dynamically adjusted usinga microprocessor using adaptation algorithm 626.

Anti-aliasing filter 622 can reject signal components with bandwidthsgreater than one-half the sampling frequency of analog-to-digitalconverter 624, as well as frequencies within one or more adjacentNyquist zones, to reduce aliasing from converting the downlink referencesignal from analog to digital. Analog-to-digital converter 624 canconvert the analog downlink reference signal to digital.

Configurable digital filter 618 can modify the downlink reference signalto generate the downlink mitigation signal as described above withrespect to configurable digital filter 504 shown in FIG. 5. The downlinkmitigation signal can remove undesirable signals generated in downlinkcommunication path 202 from the uplink signal. Digital summer 616 cansum the downlink mitigation signal with the uplink signal. An output(e₁(n)) of digital summer 616 can be the uplink signal after mitigatingundesirable signal components.

A microprocessor using adaptation algorithm 626 can iteratively adjustfrequency response w₁[n] of configurable digital filter 618 and theattenuation provided by attenuator 620 in response to e₁(n) and thedownlink reference signal. Adaptation algorithm 626 can receive e₁(n)and the downlink reference signal as inputs. Iteratively adjusting thefrequency response of configurable digital filter 618 can allowconfigurable digital filter 618 to generate a downlink mitigation signaldynamically in response to the transmission of a downlink signal.Iteratively adjusting the attenuation provided by attenuator 620 canallow attenuator 620 to equalize the signal power of the downlinkreference signal and the undesirable signals recovered by antenna 108.

FIG. 7 depicts additional circuitry to remove additional nonlineardistortion from uplink signals following active digital mitigation.Additional nonlinear distortion can result from downlink noisecomponents generated by downlink analog signal processing components indownlink communication path 202. The downlink analog signal processingcomponents can include analog filter 604, mixer 606, local oscillator608, image reject filter 700, and power amplifier 610. Image rejectfilter 700 can reject or attenuate any output signal from mixer 606 atan image frequency of the desired downlink frequency. Power amplifier610 can amplify the downlink signal to an output power for transmission.

Both the uplink signal and the downlink reference signal can include thedownlink noise components at the inputs to the frequency conversioncircuitry in uplink communication path 204 and reference path 600.Frequency conversion circuitry can include anti-aliasing filters 612,622, and analog-to-digital converters 614, 624. Frequency conversioncircuitry in the respective signal paths can create additional nonlineardistortion signals in uplink communication path 204 and reference path600 by processing downlink noise components in each signal path.

The randomized (e.g., non-periodic) nature of the downlink noisecomponents can cause randomized additional nonlinear distortion signals.Phase-shifting the additional nonlinear distortion signal traversingreference path 600 may not create a mitigation signal that can mitigatethe additional nonlinear distortion signal traversing uplinkcommunication path 204. Instead, digital summer 616 can sum theadditional nonlinear distortion signals traversing uplink communicationpath 204 and reference path 600. The output of digital summer 616 can bean uplink signal that includes the summed additional nonlineardistortion signals. To remove the summed additional nonlinear distortionsignals from the uplink signal, configurable digital filter 702 cangenerate a nonlinear distortion mitigation signal to mitigate additionalnonlinear distortion in uplink communication path 204. Digital summer616 and configurable digital filter 618 can mitigate other undesirablesignal components as described with reference to FIG. 6.

The input to digital-to-analog converter 602 can be used as a secondreference signal. Time delay component 704 can time-delay the secondreference signal. The delay can be equal to the propagation delay of thereference signal traversing reference path 600. The propagation delaycan be equal to the delay introduced by the components of both downlinkcommunication path 202 and reference path 600. Delaying the secondreference signal can ensure that the second reference signal is in phasewith the downlink reference signal traversing reference path 600.Non-linear transformation function 710 can generate a distortedreference signal from the output of time delay component 704. Thedistortion from non-linear transformation function 710 is proportionalto the additional nonlinear distortion from the downlink analog signalprocessing components and the frequency conversion circuitry in uplinkcommunication path 204 and reference path 600. Configurable digitalfilter 702 can generate a nonlinear distortion mitigation signal fromthe distorted reference signal. The nonlinear distortion mitigationsignal can mitigate the summed additional nonlinear distortion signalsfrom the output of digital summer 616 traversing uplink communicationpath 204. Digital summer 706 can sum the nonlinear distortion mitigationsignal with the uplink signal. The output of digital summer 706 can be amodified uplink signal (e₃(n)).

A microprocessor having a computer readable medium on which anadaptation algorithm 708 is stored can iteratively adjust frequencyresponse w₃[n] of configurable digital filter 702 in response to e₃(n)and the second reference signal. The inputs to adaptation algorithm 708can be modified uplink signal e₃(n) and the output of non-lineartransformation function 710. Iteratively adjusting the frequencyresponse w₃[n] can allow configurable digital filter 702 to dynamicallygenerate a mitigation signal that correlates substantially with thesummed additional nonlinear distortion signals traversing uplinkcommunication path 204.

FIG. 8 depicts additional circuitry for separately mitigating theadditional nonlinear distortion signals traversing uplink communicationpath 204 and reference path 600. Configurable digital filter 702 anddigital summer 706 can remove the additional nonlinear distortion signaltraversing reference path 600. Configurable digital filter 800 canmodify an additional reference signal to generate a reference mitigationsignal. The reference mitigation signal can mitigate signal componentsat uplink frequencies in the downlink reference signal traversing thesecond reference path. Configurable digital filter 800 and digitalsummer 802 can remove the additional nonlinear distortion signaltraversing uplink communication path 204.

Configurable digital filter 804 can modify the time-delayed referencesignal from time delay component 704. Configurable digital filter 804can attenuate the time-delayed reference signal such that the power ofthe time-delayed reference signal is equal to the power of theadditional nonlinear distortion signal traversing uplink communicationpath 204. The output signal of configurable digital filter 804 can bethe input to non-linear transformation function 806. The output signalof non-linear transformation function 806 can be the input toconfigurable digital filter 800. Configurable digital filter 800 cangenerate a distortion mitigation signal proportional to the additionalnonlinear distortion signal traversing uplink communication path 204.The distortion mitigation signal can mitigate the additional nonlineardistortion signal traversing uplink communication path 204. Digitalsummer 802 can sum the distortion mitigation signal with the uplinksignal to mitigate the additional nonlinear distortion signal traversinguplink communication path 204. The frequency response of configurabledigital filter 800 can be optimized as depicted in FIG. 7.

Configurable digital filter 702 and digital summer 706 can mitigate theadditional nonlinear distortion signal traversing reference path 600.Configurable digital filter 702 can generate a distortion mitigationsignal proportional to the additional nonlinear distortion signaltraversing reference path 600. The distortion mitigation signal canmitigate the additional nonlinear distortion signal traversing referencepath 600. Digital summer 706 can sum the distortion mitigation signalwith the downlink reference signal to mitigate the additional nonlineardistortion signal traversing reference path 600. The output of digitalsummer 706 can be a modified reference signal after mitigating theadditional nonlinear distortion signal traversing reference path 600.The frequency response of configurable digital filter 702 can beoptimized as described with reference to in FIG. 7.

Configurable digital filter 618 can generate a downlink mitigationsignal from the modified reference signal. Digital summer 616 can sumthe downlink mitigation signal with the uplink signal from digitalsummer 802. The output of digital summer 616 can be the uplink signalafter mitigating both the undesirable downlink signal components and theadditional nonlinear distortion signals traversing uplink communicationpath 204 and reference path 600.

The foregoing description of the examples, including illustratedexamples, has been presented only for the purpose of illustration anddescription and is not intended to be exhaustive or to limit the subjectmatter to the precise forms disclosed. Numerous modifications,adaptations, and uses thereof will be apparent to those skilled in theart without departing from the scope of this disclosure. Theillustrative examples described above are given to introduce the readerto the general subject matter discussed here and are not intended tolimit the scope of the disclosed concepts.

What is claimed is:
 1. A remote antenna unit, the remote unitcomprising: a downlink communication path and an uplink communicationpath; a coupling device coupled to the downlink communication path andthe uplink communication path, the coupling device configured to couplethe downlink communication path and the uplink communication path to anantenna, wherein the coupling device does not utilize a duplexer toisolate the downlink communication path from the uplink communicationpath; an active mitigation subsystem comprising: one or more highdynamic range analog-to-digital converters positioned in the uplinkcommunication path; a filter; wherein the active mitigation subsysteminputs a downlink reference signal from the downlink communication pathand the filter generates a downlink mitigation signal from the downlinkreference signal, wherein the active mitigation subsystem output thedownlink mitigation signal onto the uplink communication path.
 2. Theremote antenna unit of claim 1, the active mitigation subsystem furthercomprising: a reference path communicatively coupled with both thedownlink communication path and the uplink communication path, whereinthe filter is positioned in the reference path.
 3. The remote antennaunit of claim 1, wherein the filter adjusts a phase of the downlinkreference signal to generate the downlink mitigation signal.
 4. Theremote antenna unit of claim 1, wherein the filter adjusts a gain of thedownlink reference signal to generate the downlink mitigation signal. 5.The remote antenna unit of claim 1, wherein the downlink mitigationsignal is equal in amplitude with the downlink reference signal and 180degrees out of phase with the downlink reference signal.
 6. The remoteantenna unit of claim 1, wherein the filter comprises a configurableanalog filter.
 7. The remote antenna unit of claim 1, wherein the filtercomprises a configurable digital filter.
 8. The remote antenna unit ofclaim 1, wherein the one or more high dynamic range analog-to-digitalconverters have a dynamic range and bandwidth sufficient to directlysample incoming RF signals received by the antenna.
 9. The remoteantenna unit of claim 7, wherein the active mitigation subsystemcomprises at least one high dynamic range analog-to-digital converters.10. The remote antenna unit of claim 8, wherein the downlink referencesignal comprises an analog signal and the downlink mitigation signalcomprises a digital signal.
 11. The remote antenna unit of claim 1further comprising: one or more high dynamic range analog-to-digitalconverters positioned in the downlink communication path, the one ormore analog-to-digital converters in the downlink communication pathhaving a dynamic range and bandwidth sufficient to directly sampleincoming RF signals from a base station.
 12. A method comprising:coupling a downlink communication path of a remote unit and an uplinkcommunication path of the remote unit to an antenna through a couplingdevice, wherein the coupling device does not utilize a duplexer toisolate the downlink communication path from the uplink communicationpath; converting analog uplink communication signals traversing theuplink communication path from analog signals to a digital signals withone or more high dynamic range analog-to-digital converters positionedin the uplink communication path; converting a downlink reference signalfrom the downlink communication path to a downlink mitigation signal andoutputting the downlink mitigation signal onto the uplink communicationpath.
 13. The method of claim 12, wherein the one or more high dynamicrange analog-to-digital converters have a dynamic range and bandwidthsufficient to directly sample incoming RF signals received by theantenna.
 14. The method of claim 12, further comprising: convertingdownlink signals traversing the downlink communication path from analogsignals to a digital signals using an analog-to-digital converter havinga dynamic range and bandwidth sufficient to directly sample incoming RFsignals from the base station.
 15. The method of claim 12, wherein areference path communicatively couples the downlink communication pathto the uplink communication path, wherein converting the downlinkreference signal to the downlink mitigation signal is performed by thereference path.
 16. The method of claim 15, wherein a filter ispositioned in the reference path, wherein converting the downlinkreference signal to the downlink mitigation signal is performed by theconfigurable filter.
 17. The method of claim 16, wherein the filtercomprises a configurable analog filter.
 18. The method of claim 16,wherein the configurable filter comprises a digital filter.
 19. Themethod of claim 16, wherein the filter adjusts a phase or gain of thedownlink reference signal to generate the downlink mitigation signal.20. The method of claim 12, wherein the downlink mitigation signal isequal in amplitude with the downlink reference signal and 180 degreesout of phase with the downlink reference signal.